1. Field of the Invention
The present invention relates to systems and methods for simulating certain anatomic features of the human eye to allow trainees to practice invasive procedures upon a realistic anatomic replica. In particular, the present invention provides in one embodiment a simulation of a human cornea to permit incisions to be practiced thereupon.
2. Description of the Related Art
It is well understood in the ophthalmological art that the lens contributes only one third of the total focusing power of the eye, while the remaining two-thirds arises from the convex shape of the anterior corneal surface. It is further understood that very small changes in corneal shape may have a dramatic effect on the precision with which light rays are brought to the focus upon the retina. Incisions made in the cornea or anterior sclera during ophthalmological procedures, therefore, may change the refraction of the eye. It appears that surgically induced change in corneal contour is less significant for more peripheral incisions in the sclera or limbus than for those incisions that involve the cornea. A substantial literature in the ophthalmological art supports the premise that smaller incisions are associated with less surgically induced change in corneal contour, earlier visual recovery after surgery, more stable refraction, and better uncorrected postoperative visual acuity. Furthermore, it has been determined that the placement of sutures to close access incisions may induce astigmatism. Although for larger incisions, suture placement has been necessary to close the path between the interior of the eye and its external surface, placing sutures in the surface of the eye may combined with natural wound healing characteristics to alter the shape of the eye and thereby induce astigmatism. For all these reasons, surgeons have determined that minimizing the size of corneal incisions would be desirable.
Surgical access to the interior portions of the eye has been the subject of intensive research to discover the most effective and least traumatic technique. Scleral tunnel incisions were introduced in the early 1980s in order to provide better wound healing with less surgically induced astigmatism; these incisions permitted wider surgical exposure for cataract extraction and were modified for phacoemulsification. In 1990, the sutureless incision was developed, which utilized a longer scleral tunnel with a grooved floor in the meridian of the incision. This incision could be stretched to admit a folded lens following phacoemulsification, and could remain unsutured thereafter. The corneal entry point of this tunneled incision was shaped as a one-way valve or corneal lip so that the incision would self-seal. The temporal, sutureless, clear corneal incision for cataract surgery was described in 1992. It has now become a favored technique for cataract surgery internationally in conjunction with foldable or small-incision intraocular lenses. The development of sutureless, astigmatically neutral incisions has combined with advances in intraocular lens technology to permit major advances in the surgical treatment of cataracts. Clear corneal incisions have gained ascendancy over recent years for a variety of cataract extraction techniques.
For cataract surgery using small-incision techniques, the incision for which the surgical tools are inserted generally approximates the circumference of the tools that are inserted therethrough. If the incision is too small, corneal tissue surrounding the incision may be damaged by stretching or by thermal injury. If the incision is too large, leakage from the unsutured passageway may occur after surgery with potentially disastrous consequences. The angle of the incision is also important to allow optimal surgical access while still permitting self-sealing. A number of variations on surgical techniques exists for performing clear corneal incisions. An initial incision method involved making incision in a single plane. Subsequently, a perpendicular groove of 300 to 400 microns in depth was added to the incision to form a superior lip, resulting in less tendency for tearing. Special surgical tools may be used to form these delicate incisions. For example, a diamond knife which is beveled on all edges may be used whose dimensions are specifically constructed so that the tip of the diamond is a preselected distance (e.g., 1.75 mm ) from a line joining the shoulders of the blade. Using such a knife, an incision may be constructed by applanation of the wall of the eye, so that the tip is at the anterior edge of the vascular arcade. From that position, the knife may be advanced in the plane of the cornea until a line that joins the shoulders reaches the incision, at which point the tip is tilted down through Descemet""s membrane before the initial plane is re-established, at which point the knife is inserted to the hilt. As a result, a rectangular incision 3 mm wide and 2 mm long is formed. It is understood that incisions of less than 3 mm width in the peripheral cornea are astigmatism neutral as long as they are constructed with sufficient accuracy. Other methods for forming clear corneal incisions are familiar to skilled practitioners in the field. Often, anatomic landmarks, such as the angle of the sclera, the angle of the iris or the curvature of the cornea, are used to guide the direction for inserting the ophthalmological scalpel as the incision is formed. For many clear corneal incisions, widths between 2.5 mm and 3 mm are commonplace. These incisions permit subsequent access to the cataract using the variety of techniques well-known in the art. While the incisions described above are generally familiar to ophthalmologic surgeons, innovation in technique and instrumentation is ongoing. New surgical incisions and new surgical tools may be devised to facilitate access to intraocular structures through the clear cornea or through other anatomic areas of the eye.
The size of these incisions, the complexity of their geometry and their location in the optically sensitive corneal region makes it imperative that they be made cleanly and accurately. There is little if any room for error. A poorly made incision may require corrective steps to be taken that eliminate the incision""s purported advantages and that introduce other potential complications. Without both training and practice, it is difficult for physicians to form these incisions consistently and precisely. Not only must trainees and less experienced surgeons be able to practice established techniques using commonplace instrumentation, but also must well established surgeons have an opportunity to practice in order to learn a new surgical method or to try out a new surgical tool.
Currently, a surgeon wishing to learn an unfamiliar skill and gain proficiency therein has a limited number of options for learning and practicing. In time-honored manner, the surgeon may practice in vitro using an animal eye or may initially try out an instrument or practice a skill on a patient during actual surgery. There are limitations to both options. The animal eye in a fresh or preserved state may lack of the surgical characteristics of a living human patient""s eye. The animal eye may also introduce sanitary and hazardous material issues. Using the patient undergoing eye surgery as a laboratory for learning new skills or experimenting with new instruments is even more undesirable.
There exists in the art, therefore, a need for a training system that simulates surgical characteristics of the human eye, especially those characteristics relevant to trans-corneal incisions. Other simulation systems for training surgeons exist for specific body parts. The development of endoscopic surgery, for example, has given rise to a number of training devices to teach surgeons endoscopic skills. For ophthalmological surgery, a device called xe2x80x9cMarty the Surgical Simulatorxe2x80x9d is available for training surgeons to operate upon the lens. xe2x80x9cMartyxe2x80x9d provides a synthetic cataract within a simulated eyeball upon which a surgeon can practice cataract procedures. However, xe2x80x9cMarty,xe2x80x9d covered by U. S. Pat. Nos. 4,762,495, 4,762,496, 4,865,551, 4,865,552, and 5,261,822, is not configured to be used for incision training. There remains in the art, therefore, a need for a practice system that replicates the anatomic and surgical characteristics of the eye as encountered by surgeons carrying out clear corneal surgery in actual patients. This need will continue to grow as the complexity of surgical methods and instrumentation for trans-corneal surgery continues to advance.
It is therefore an object of the present invention to provide a system for ophthalmological surgical training that includes a base, a removable corneal portion configured for placement over the upper portion of the base, and a cover that has an aperture in its top so that placing of the cover over the base permits the corneal portion to extend through the aperture, and results in securing the corneal portion across the aperture between the upper portion of the base and the top end of the cover. In certain embodiments, the top of the cover has a curvature that approximates an angle of curvature of the human sclera. In certain embodiments, the cover includes a flange that facilitates placement of the cover onto and removal of the cover from the base by the user. In certain embodiments, a mechanism may be included to permit a secure engagement between the cover and the base. This mechanism may include a groove at the lower portion of the base and a protrusion at the bottom end of the cover for removable engagement with the groove. This mechanism may, alternatively, include a plurality of threads along a portion of the base and complementary threads along an interior surface of the cover. In certain embodiments, the corneal portion is made from a material which simulates a surgical characteristic of human corneal tissue when incised.
It is a further object of the present invention to provide a simulation system for ophthalmological surgery that includes a central member that has a top surface geometrically configured to simulate a human iris, a housing that may cover the central member that has a top portion configured to simulate the anterior sclera of the human eye and that has an aperture in its center so that the top surface of the central member can protrude through when the housing is positioned to cover the central member, and an artificial cornea removably affixable to the top surface of the central member. In certain embodiments, the artificial cornea affixed to the top surface forms a chamber therebetween that is substantially similar in dimension or in mechanical properties to the anterior chamber of the human eye. In certain embodiments, the artificial cornea may be fabricated from a material that simulates a surgical characteristic of the human cornea. In certain embodiments, the central aperture of the housing is dimensionally adapted for holding the artificial cornea and the top surface tightly therein. In certain embodiments, the central member has a bottom end that is stabilizable upon a work surface. In other embodiments, the housing has a bottom surface that is stabilizable upon the work surface. In certain embodiments, the top portion of the housing includes a sloped periphery surrounding the central aperture that is geometrically configured to simulate a slope of the anterior sclera of the human eye. In certain embodiments, the engagement of the housing with the artificial cornea forms a smooth surface that simulates a shape of the anterior aspect of the human eye and further produces within the chamber a pressure that is substantially similar to the anterior chamber pressure of the human eye. The housing may bear an affixation means that mates with a complementary affixation means on the central member of the base, allowing the central member to be removably affixed to the housing and to be stably encased therein. In certain embodiments, an artificial pupil may be included, or an artificial lens may further be included that is accessible through the artificial pupil.
It is also object of the present invention to provide a system for practicing a corneal incision that includes a practice cornea, an artificial iris upon which the practice cornea may be removably seated, and an artificial sclera detachably affixable to the artificial iris. In this embodiment, the artificial iris and the artificial sclera may simulate a dimensional and a geometric characteristic of the human eye; furthermore, the practice cornea may simulate a dimensional and a mechanical characteristic of the human cornea; and furthermore, the assembly of the practice cornea, the artificial iris, and the artificial sclera may simulate in size and shape a portion of the human eye, thereby permitting practicing the corneal incision in a realistic manner. In certain embodiments, the artificial sclera may include a central aperture through which the practice cornea seated upon the artificial iris may protrude in an anatomically correct geometric configuration; in this embodiment, the central aperture further stabilizes the practice cornea upon the artificial iris. In certain embodiments, the central member may bear a top surface that forms the artificial iris. In these embodiments, the central member may be dimensionally adapted for directing the practice cornea seated upon the artificial iris into the aperture. In these embodiments, further, the central member may be removably affixable within the housing; such affixation may serve to stabilize the artificial cornea securely upon the artificial iris. In one embodiment, there may be included in the system a simulated feature of the human face.
It is an additional object of the present invention to provide methods for training surgical incision-making. In one practice of the present invention, the method includes providing a practice cornea affixed to an artificial iris in an anatomically correct position; providing a surgical tool suitable for making an incision in a human cornea; determining a surgically proper angle for incising a human cornea; and incising the practice cornea by inserting the surgical tool into it at the surgically proper angle. In one practice of the method, the step of evaluating the incision in the practice cornea to determine a morphological characteristic thereof may be included. In certain practices, the surgically proper angle is substantially similar to the angle of curvature of the human iris. In other practices, the surgically proper angle is substantially similar to the angle of curvature of the human sclera. A practice of the present method may further include the following steps: removing the practice cornea; affixing an intact practice cornea to the practice iris in an anatomically correct position; and incising the intact practice cornea by directing the surgical tool into the intact practice cornea at a preselected angle. This practice may further include the evaluation of the intact practice cornea after it has been incised in order to determine a morphological characteristic thereof.
These and other aspects of the invention will be more fully understood by referring to the following detailed description and the accompanying drawings, wherein like numbers reference like features.